This invention relates to a liquid crystal display device and, in particular, to a liquid crystal shutter including a nematic liquid crystal having a frequency dependent dielectric anistropy.
Prior art liquid crystal shutters are arranged so that a nematic liquid crystal material having a frequency dependent dielectric anistropy is enclosed in a space between opposed cooperating electrodes. A high frequency signal of about 70 KHz and a low frequency signal of about 500 Hz are selectively applied to the electrodes in order to change the molecular configuration of the liquid crystal material and, by doing so, open or close a shutter opening to light.
A liquid crystal shutter operating in this manner is disclosed in Japanese Patent Laid-Open Publication No. 193522/83. This liquid crystal shutter improved response speed by about one hundred (100) times compared with conventional liquid crystal shutters in which the molecular orientation of the liquid crystal material was changed depending on the voltage level. This development made it possible to use the shutter to expose the photosensitive surface of a rotating drum and to print data at high speeds.
When the high frequency signal used to open the shutter is applied continuously to the liquid crystal material over, a regular interval, mechanical vibrations due to resonance of unknown origin arise on the electrode substrate used to assemble the liquid crystal cells. As a result, the molecular orientation of the liquid crystal material changes over time and the amount of light transmitted through the shutter opening also changes. Variation of the amount of light transmitted is disadvantageous and impedes use of such shutters.
Accordingly, it is desirable to provide a liquid crystal shutter wherein the amount of light transmitted is stable over time and which overcomes the disadvantages inherent in prior art liquid crystal shutters.